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    <meta charset="UTF-8">
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    <title>Document</title>
    <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
</head>
<body>
    <table id="tab">
        <tbody>
            <tr>
                <td>第一行</td><td>第一行</td>
            </tr>
            <tr>
                <td>第二行</td><td>第二行</td>
            </tr>
            <tr>
                <td>第三行</td><td>第三行</td>
            </tr>
            <tr>
                <td>第四行</td><td>第四行</td>
            </tr>
            <tr>
                <td>第五行</td><td>第五行</td>
            </tr>
            
        </tbody>
        
    </table>
    <script>
        var trArr = $("tbody tr");
        var length = $("tbody tr").length;
        for(let i = 0; i < length;i++){
            if(i % 2 != 0){
                trArr[i].style.color = "red";
            }
        }
       // $("tr:odd ").css("color","red")
    </script>
</body>
</html>